If you desire to think regarding a car alarm in its simplest shape, it is not anything but one or additional sensors associated to some type of alarm bell. The extremely simplest alarm would have a button on the driver's door, and it would be wired so that if someone opened the door the siren would begin howling. You could put into practice this car alarm with a knob, a pair of pieces of wire and a siren. Some car alarm tracker systems are used by the Police to pull through stolen vehicles without you having to notify them of the cars locality, the Police can login on a PC and outlook a map. On a more vital system you would have to look on your PC and phone the Police, prefer a system that permits the car to be immobilizer by the use of text message first so that the car is motionless when you call them.